PM8805 datasheet(32/45 Pages) STMICROELECTRONICS

32 / 45 page

PM8805 overview

PM8805

32/45

DS12813 Rev 1

is capable of providing all the power it needs. It is also assumed that an auxiliary source is

always capable of providing the requested power.

See Table 12 for the minimum information needed for confirming the requested class for

each PD class.

T2 indication is directly related to the number of powered pairs, providing a low level output

only when both the active bridges are on. When an auxiliary connection is present, T2 is set

to 1, since both front and rear Aux connections typically bypass the active bridges.

4.13

Standby and MPS

When a PoE PD system goes into standby its power consumption may be very low and for

this reason it may be disconnected by the PSE.

To avoid PD disconnection the PM8805 features a Maintain Power Signature (MPS) current

control.

Asserting the STBY pin, the device starts drawing a current whose profile is determined by

the detected PSE Power Type, the length of the first Class Event and the number of active

pairs when entering STBY mode.

Table 11. PM8805 type signals description table

Identification

Bridges

Class events

Notes

Type 1 (13W)

0 or 1

Legacy PD type

Type 2 (25.5W)

2, 3

Legacy PD type

Type 3 (51W)

New PD type

Type 4 (71W)

≥ 5

New PD type

Type3 on 4-pair (13W), or

Legacy 4-pair (Type 1

class)

0 or 1

New PD type

Type3 on 4-pair (25.5W),

or Legacy 4-pair (Type 2

class)

2, 3

New PD type

Rear AUX

any

AUX present

Front AUX

Table 12. Minimum information needed for confirming requested class

PD requested class

Requested class confirmation

Class 0-3

Always

Class 4

(T0 or T1)=0

Class 5-6

T1=0

Class 7-8

T0 or T1)=0

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